KR20170098911A - Method and device for reducing heavy polycyclic aromatic compounds in hydrocracking units - Google Patents

Abstract

The present invention is directed to a method and apparatus that can reduce the concentration of heavy polycyclic aromatic compounds (HPNA) in the recycle loop of hydrocracking units comprising fractionation columns. According to the method of the present invention, a stream is withdrawn from the fractionation column in the region of the at least one tray located between the feed tray and the withdrawal tray for the heaviest distillate fraction, and the stream is introduced into the stripping gas Lt; RTI ID = 0.0 > stripping < / RTI > The separated gas effluent is advantageously recycled to the column as stripping gas, the liquid fraction is recycled to the hydrocracking stage and the residual oil is purged in the stripping step.

Description

METHOD AND DEVICE FOR REDUCING HEAVY POLYCYCLIC AROMATIC COMPOUNDS IN HYDROCRACKING UNITS FIELD OF THE INVENTION The present invention relates to a method and apparatus for reducing heavy polycyclic aromatic compounds in hydrocracking units,

The present invention relates to a process and apparatus for reducing the concentration of heavy polycyclic aromatic compounds (HPNA) in a recycle loop of hydrocracking units.

Hydrocracking processes are routinely used in tablets that modify hydrocarbon mixtures with products that can be easily upgraded. These processes may be used, for example, to convert light oil such as gasoline into lighter oil (LPG). However, the processes may be more generally carried out in the presence of heavier feeds (for example oil oils or heavies, such as gas oils obtained from vacuum distillation or effluents from Fischer-Tropsch units) into gasoline or naphtha, kerosene or gas oil It is used to convert. This type of process is also used to produce oil.

To increase the conversion of hydrocracking units, a portion of the unconverted feed is recycled to the reaction section or stand-alone reaction section it has already passed through. This causes unwanted accumulation in the recycle loop of polycyclic aromatic compounds formed in the reaction section during the decomposition reactions. These compounds adversely affect the hydrocracking catalyst, which reduces cycle time as well as catalyst activity. The compounds may also precipitate or precipitate in the cold parts of the unit, causing disruptions.

Thus, there is a need to improve the hydrocracking process to reduce the formation of polycyclic aromatics or to eliminate it, without reducing the yield of the producible products.

HPNA compounds are thus defined as polycyclic or polynuclear aromatic compounds containing several condensed benzene nuclei or rings. It is commonly known as HPA, heavy polynuclear aromatic, or PNA or HPNA.

Typically, HPNA, known as heavy, contains at least four or even at least six benzene rings in each molecule. Compounds having less than six rings (e.g., pyrene derivatives) can be more easily hydrogenated and therefore less likely to adversely affect the catalyst. As a result, for example, compounds which are most easily discernible and quantifiable by chromatography, such as coronene (compound containing 24 carbon atoms), dibenzo (e, ghi) perylene (26 carbons Compounds representative of families including six or more aromatic rings such as naphtho [8,2,1, abc] coronene (30 carbon atoms) and ovalene (32 carbon atoms) I am especially interested in.

Applicant's patent US 7 588 678 describes a hydrocracking process with an unconverted 380 ° C + fractional recycle wherein HPNA compounds are removed from the recycled fraction by the adsorbent. Other techniques for reducing the amount or eliminating HPNA are described in the prior art for that patent, for example, reduction through precipitation followed by hydrogenation or filtration.

Patent US 4 961 839 discloses a process for converting per-pass using a high flow rate of hydrogen in the reaction zone by vaporizing a large proportion of the hydrocarbons sent to the column to separate the products and concentrating the polycyclic aromatics in the less heavier fractions extracted from the column RTI ID = 0.0 > hydrocracking < / RTI > In the process, the heavier fraction is withdrawn from the level of the plate located below the point of supply and above the point for withdrawing the gas oil distillate; The heavy fraction is recycled to the hydrocracking furnace. The bottoms (residues) of the column are recycled directly to the fractionation column. This type of technique can actually reduce the concentration of HPNA in the recycle loop to the reactor, but leads to a high cost associated with the amount of hydrogen and a considerable yield loss.

Patent applications WO 2012/052042 and WO 2012/052116 (corresponding to US-2013/0220885) describe a hydrocracking process in which the bottoms of the fractionating column (residual oil) are stripped as a countercurrent in a stripping column. The hard fraction obtained after stripping is sent to the fractionation column and at least a portion of the heavy fraction obtained from the stripping is purged and other portions of the fraction are selectively recycled to the stripping column.

The processes caused improvements in the reduction of HPNA, but often hampered yield and cost.

The process of the present invention can be used not only to reduce the amount of purged residual oil to concentrate the polycyclic aromatic hydrocarbons in the unconverted fraction (residual oil) and to increase the conversion to remove the unconverted fraction, Can be used to improve the yield and / or catalyst cycle time of the products that can be improved (e.g., by preventing overdissipation of the gas oil) compared to processes. The present invention also has the advantage of significantly reducing the amount of HPNA that is refractory to reactions occurring during hydrocracking and which contains at least six aromatic rings provided in the hydrocracking furnace.

The process according to the invention is characterized in that the sidestream is positioned in the column below the feed and below the draw-out for the heaviest gas oil distillate, stripped off the withdrawn fraction and then stripped, preferably as stripping gas, Based on returning all or part to the column. This causes super-evaporation. Separation is carried out by combining a stripper stripping the withdrawn fraction with a fractionation column. The stripper also accommodates a portion of the stripped residue. Thus, spreading is carried out at the level of the stripper.

This process also has the advantage of not introducing excess gas into the column by injecting stripping gas (e.g. steam) outside the process. Another advantage is to further improve the improvement of the product by treatment of residual oil during stripping, which is considered waste (purge) in the prior art.

More precisely, the present invention relates to a process for hydrocracking an oil feed comprising at least 10% by volume of compounds boiling above 340 DEG C, said process comprising a hydrocracking step, The hydrocracking step followed by the separation of the gas from the cracked effluent, followed by fractionation of the effluent from which at least one distillate and residue are separated, wherein a portion of the residual oil is recycled to the hydrocracking step Wherein said fractionation step comprises distillation in a column with plates, wherein in said column:

The at least partially vaporized effluent is fed to the column through a feed plate,

The distillate is withdrawn from the level of the drawing plate,

The residual oil is discharged at the discharge point,

- Stripping gas is injected at the injection point located below the feed plate,

In the process

A portion of the stream present at the level of at least one plate located between the feed plate and the plate for withdrawing the heaviest distillate fraction is withdrawn from the column,

All or a portion, preferably all, of said withdrawn stream is stripped in an external stripping step by a stripping gas in the presence of a portion of the residual oil discharged from said column, a gas effluent and a liquid fraction are obtained,

All or part, preferably all, of the separated gas effluent is recycled to the column,

All or part, preferably all, of said liquid fraction is recycled to said hydrocracking step,

Residual oil is purged in the stripping step.

Advantageously, a portion of the stream located above the level of the plate located on the supply plate and near the supply plate, preferably at the level of the plate closest to the supply plate, is withdrawn from the column.

The withdrawn stream has an HPNA concentration of less than 500 ppm by weight, preferably less than 350 ppm by weight, very preferably less than 200 ppm by weight. It usually has a proportion of at least 70% by weight of unconverted hydrocarbons, preferably at least 80% by weight of unconverted hydrocarbons, very preferably at least 90% by weight of unconverted hydrocarbons.

Advantageously, all or a portion, preferably all, of said gas effluent is recycled to said column under said feed plate.

Most preferably, all or a portion, preferably all, of the gas effluent is recycled to the column as stripping gas, preferably as the only stripping gas. If necessary, it may be used with other stripping gases.

According to the present invention, all or a portion, preferably all, of the liquid effluent separated in the stripping step is preferably directly recirculated to the hydrocracking step.

Preferably, a portion of the residual oil discharged from the column is recycled to the hydrocracking stage.

Preferably, the process operates in the presence of the stripping gas injected into the fractionation step. Preferably, it is preferably steam at a pressure in the range of 0.2 to 1.5 MPa.

The stripping gas injected into the external stripping step is preferably steam at a pressure preferably in the range of 0.2 to 1.5 MPa.

The hydrocracking step is carried out in a conventional manner at a temperature above 200 ° C, pressure above 1 MPa, space velocity of 0.1-20 h ^-1 , and H ₂ / hydrocarbon volume ratio of 80-5000 NL / L.

The invention also relates to a facility comprising:

- a hydrogenolysis section (2) having an inlet line (1) for the feed and an inlet line (8) for hydrogen,

Optionally followed by a zone (4) for separating the effluent to separate the gas fractions,

Followed by a fractionation section (12) comprising at least one distillation column with plates, said column comprising:

   at least one line (11) for the introduction of at least partially vaporized hydrocracked effluent into at least one feed plate,

   o at least one line (14) for withdrawing at least one distillate from the level of the withdrawal plate,

   o at least one line (15a) for discharging residues,

- at least one line (19) for injecting stripping gas, the injection point being located below said feed plate,

The facility includes:

At least one line (20) for withdrawing a portion of the stream present at the level of the at least one plate located between the feed plate and the plate for withdrawing the heaviest distillate fraction,

A line for introducing a portion of the residual oil discharged from the column, a line for injecting stripping gas, an outlet line for gas effluent 22), and an outflow line (27) for the liquid fraction, the stripper (25) outside the column,

- a line (22) for recirculating all, or preferably all, of said gas effluent to said column,

A line 27 for recirculating all, or preferably all, of the liquid fraction to the hydrocracking step,

- Includes a line (24) for purging a portion of the residue.

Advantageously, the draw plate 20 is at the level of the plate closest to the feed plate.

Preferably, said lines (22, 19) are merged and said gas effluent is a stripping gas; The line 22 feeds the gas effluent to the column at the stripping gas injection point (line 19).

Preferably, the facility further comprises at least one line (23, 18) for recycling a portion of the residual oil discharged from the column to the hydrocracking step.

In a preferred arrangement, there is no line for recycling the separated liquid fraction (line 27) in the stripping step to the fractionation column.

The invention will be better understood from the description of the following drawings.

In the text, the feed is defined by the T5 boiling point (as described below). The feed conversion is defined for the cut point of the residual oil. Untransformed fractions are referred to as residual oils. The transformed fraction contains fractions (target) sought by the purifier.

The purged portion refers to the portion from the process.

The invention will be better understood from the description of the following drawings.

Figure 1 shows the prior art.
Figure 2 shows the invention.
Fig. 2 will be understood in combination with Fig. 1, more precisely in combination with the essential elements of Fig. 1, cited in the claims.

Figure 1 provides a flowchart for a prior art hydrocracking process. For ease of reading, the description of the conditions used has been moved to another part of the text below.

(Line 1) consisting of hydrocarbons and / or minerals of oil origin or of synthetic hydrocarbons having biological sources is fed via line 7 to line 5 (recycle) and / or line 6 Hydrogen). ≪ / RTI >

The thus formed feed / hydrogen mixture is sent to the hydrocracking section (2). This section includes one or more fixed beds or ebullated bed reactors.

When the hydrocracking section comprises one or more fixed bed reactors, each reactor may comprise one or more catalyst layers which effect hydrocracking of the hydrocarbons of the feed to form lighter hydrocarbons.

When the hydrocracking section comprises one or more boiling-bed reactors, the liquid, solid and gas-containing streams travel vertically through the reactor including the catalyst bed. In the layer, the catalyst is maintained in a random motion in the liquid. Thus, the total volume of catalyst dispersed through the liquid is greater than the volume of the catalyst when stopped. This technique has been widely described in the literature.

A mixture of liquid hydrocarbons and hydrogen passes through the bed of particles of the catalyst at such a rate that the particles move randomly and are suspended in the liquid. In the equilibrium state, the expansion of the catalyst bed in the liquid is controlled by the flow rate of the recirculating liquid so that the majority of the catalyst does not exceed a prescribed level in the reactor. The catalyst is preferably in the form of extrudates or beads having a diameter in the range of 0.8 mm to 6.5 mm in diameter.

In the boiling layer process, large amounts of hydrogen gas and hard hydrocarbon vapors rise through the reaction zone and thereafter in the catalyst free zone. A portion of the liquid from the catalyst zone is recycled to the bottom of the reactor after separating the gas fractions and a portion is usually withdrawn from the reactor as product at the upper end of the reactor.

The reactors used in the boiling layer process generally include a central vertical recirculation conduit serving as a flow tube for recirculating liquid from the non-catalytic region located above the boiling layer of the catalyst through a recirculation pump that can be used to recycle the liquid in the catalytic region . Liquid recirculation means that a uniform temperature can be maintained in the reactor and the catalyst layer can be maintained in suspension.

The hydrocracking section may be preceded or included by one or more of the hydrotreating catalyst (s) layers.

The effluent from the hydrocracking section 2 is sent to the separation zone 4 via line 3 to collect the gas fraction 5 with the liquid fraction 9 on the one hand. The gas fraction (5) contains an excess of unreacted hydrogen in the reaction section (2). It is generally combined with fresh hydrogen reached via line 6 to be recycled as described below.

The liquid fraction 9 may be any means 10 that may be associated with the exchanger (not shown), for example at least partially vaporizing it prior to feeding it to the fractionation section 12 via line 11. [ .

The fractionation section 12 includes one or more distillation columns with plates and contact means to separate the various improvable oils (distillate) drawn by the lines 13, 14, as well as other optional side streams do. This oil has a boiling point range, for example, in gasoline, kerosene and gas oil ranges.

The heavier untransformed fraction (residual oil) is recovered from the bottom of the column (line 15a).

The stripping gas may be injected through line 19. [ This line is located between the plate for supplying the hydrocracked effluent (line 11) and the residual oil discharge point (line 15a).

A portion of the residue can be purged through line 16 and the other portion recycled to the hydrocracking section through lines 23 and 18 and the other portion recycled to the fractionation section (line 15b).

According to Figure 1, a portion of the residual oil (line 15b) from line 15a is mixed with the feed (line 9) upstream of the furnace 10 of the fractionation section and recycled as a mixture towards the fractionation section ).

The purge 16 can be used to remove at least a portion of the HPNA compounds that can accumulate, especially in this recycle loop, without this purge.

The region (E) shown in the outline in FIG. 1 defines a portion changed by the subject of the present invention.

Figure 2 presents the present invention. The foregoing elements will not be described here again. It should be noted that line 15b (recirculation of residual oil to the fractionation column) is preferably omitted from the present invention.

The fractionation section 12 comprises a single fractionation column. However, the present invention may be implemented with several differentiating columns, and at least one column will then comprise zone (E) according to the invention.

The previously at least partially vaporized liquid fraction 11 (hydrocracked effluent) is fed to fractionation section 12.

The side stream (line 20) is positioned at the level of one of the plates of the column. One or more side streams can be positioned at the level of the column. Thus, a portion of the stream present at the level of at least one plate located between the plate for feeding the effluent and the plate for withdrawing the heaviest distillate fraction is withdrawn.

This side stream (line 20) is preferably close to the feed plate. Preferably, a portion of the stream present at the level of the plate closest to the feed plate is withdrawn from the column.

The withdrawn stream has a low concentration of HPNA of less than 500 ppm by weight, preferably less than 350 ppm by weight, very preferably less than 200 ppm by weight, most frequently at least 70% by weight of unconverted hydrocarbons, preferably at least 80% The side stream (line 20) is positioned so as to have a large proportion of unconverted hydrocarbons in the hydrocracking section of the converted hydrocarbons, very preferably at least 90% by weight of the unconverted hydrocarbons.

To meet this criterion, the side stream (line 20) is preferably positioned above the feed plate, preferably at the level of the plate closest to the feed plate.

The withdrawn stream (line 20) is introduced to the level of the plate in the external stripper 25. It is stripped at a stage known as an external stripping step using stripping gas (supplied via line 26). All or part of the separated gas effluent is recycled to the column; According to Fig. 2, all of the gas effluent is recycled.

The gas effluent (all according to FIG. 2) is recycled (line 22) below the plate from which the stream is withdrawn and to the column under the hydrocracked effluent feed plate.

Particularly advantageously, the recycled gas effluent is used as a stripping gas in the column. Thus, it enters the column at the point of injection for the stripping gas (line 19). The injection point is located below the supply plate and above the residual discharge point. It is preferably near the point for discharging residual oil from the bottom of the column.

Preferably, the recycled gas effluent is used only as a stripping gas; However, other stripping gas may be supplied if necessary.

This other stripping gas (line 19) injected into the column is advantageously steam, preferably at a pressure in the range of 0.2 to 1.5 MPa, preferably low pressure steam.

A portion of the residual oil discharged from the fractionation column (line 15a) is also introduced into the external structure stage (stripper 25) (line 16). This introduction is carried out at the level of the plate located below the plate to introduce the withdrawn stream from the fractionation column.

Advantageously, the residual oil spread is carried out at the level of the stripping step (line 24); Thus, preferably, the residual oil from the fractionation column is not purged.

All or a portion of the liquid effluent (line 27) is recycled directly to the hydrocracking step. This effluent is removed from the stripper 25 at the level of the plate located between the plate for introducing the withdrawn stream (supplied via line 20) and the plate for introducing the residual oil (supplied via line 16). According to Fig. 2, all of the liquid effluent (line 27) is mixed with the recycled residue portion (line 23) and the mixture is recycled to the hydrocracking stage (line 18).

The lateral stripper 25 functions with the injection of stripping gas (line 26). This gas is preferably low pressure steam, preferably at a pressure in the range of 0.2 to 1.5 MPa.

Description of Conditions and Separation Steps for Hydrocracking (2)

This description shows conventional implementation conditions that can be applied to both FIG. 1 (prior art) and the present invention (FIG. 2).

Supply:

A wide variety of feeds may be processed in hydrocracking processes. Generally, it contains at least 10% by volume, generally at least 20% by volume, often at least 80% by volume, boiling above 340 ° C.

The feed may be a product such as, for example, an LCO (light gas oil obtained from a light cycle oil-catalytic cracking unit), an atmospheric distillate, a vacuum distillate such as a DC distillation or FCC, coking or pyrolysis visbreaking, as well as from units for the extraction of aromatics from the lubricating oil base or from solvent dewatering of the lubricating base oil or from virtually fixed bed or boiling layer hydrogen conversion or AR The feedstock may be feedstocks obtained from distillates resulting from processes for the desulfurization of deasphalted oil and / or processes for desulfurization of VR (reduced pressure residues) and / or deasphalted oil, or the feed may be substantially deasphalted oil, Or any mixture of the feeds quoted above. The list is not limited.

Typically, the feeds have a T5 boiling point above 150 DEG C (i.e., 95% of the compounds present in the feed have a boiling point above 150 DEG C). In the case of gas oil, the T5 point is generally about 150 ° C. In the case of VGO, T5 is generally higher than 340 占 폚, and even higher than 370 占 폚. Thus, the feedstocks that can be used can fall into a wide range of boiling points. This range is generally from gas oil to VGO and includes other feeds such as LCO and all possible mixtures.

The nitrogen content of the treated feeds in the hydrocracking processes is usually in the range of greater than 500 ppm by weight, generally in the range of 500 to 10000 ppm by weight, more typically in the range of 700 to 4500 ppm by weight, ppm. < / RTI >

The sulfur content of the feeds treated in the hydrocracking processes is usually in the range of 0.01 to 5 wt%, generally in the range of 0.2 to 4 wt%, and more usually in the range of 0.5 to 3 wt% Range. The feed may optionally contain a metal. The cumulative nickel and vanadium content of the feeds treated in the hydrocracking processes is preferably less than 10 ppm by weight, preferably less than 5 ppm by weight and even more preferably less than 2 ppm by weight. The asphaltene content is generally less than 3000 ppm by weight, preferably less than 1000 ppm by weight, more preferably less than 300 ppm by weight.

Guard layers

When the feed contains resins and / or compounds of the asphaltene type, it is advantageous to first pass the feed over a bed of catalyst or adsorbent different from the hydrocracking or hydrotreating catalyst. The catalysts or guard layers used are shapes of spheres or extrudates. Other shapes may be used. Particularly possible shapes that may be used are included in the following non-limiting list: hollow cylinders, hollow rings, Raschig rings, toothed hollow cylinders, crenelated hollow cylinders, pentarings Known wheels, cylinders with multiple holes, etc.

These catalysts may be impregnated with phases that may or may not be active. Preferably, the catalysts are impregnated with a hydrodehydrogenating phase. Very preferably, a CoMo or NiMo phase is used. These catalysts may also have macroporosity.

Operating conditions:

Operating conditions such as temperature, pressure, hydrogen recycle ratio, or space velocity per hour may vary widely depending on the nature of the feed, the quality of the desired products, and the facility available to the purifier. Hydrocracking / hydrogen conversion catalysts or hydrotreating catalysts generally have a boiling point of greater than 1 MPa, preferably greater than 1 MPa, at a temperature in the range of greater than 200 ° C, often in the range of 250 ° C to 480 ° C, advantageously in the range of 320 ° C to 450 ° C, Often in the range of 2 to 25 MPa, preferably in the range of 3 to 20 MPa, in the presence of hydrogen, and the space velocity is in the range of 0.1 to 20 h ^-1 , preferably 0.1 to 6 h ^-1 range, in the range of more preferably 0.2 ~ 3 h ^-1, in the range of in the range of l volume of the l / hydrocarbon ratio of hydrogen 80 ~ 5000 l / l, typically 100 ~ 3000 l / l The amount of hydrogen introduced.

These operating conditions used in hydrocracking processes generally yield conversions per pass to converted products in the range of greater than 15%, more preferably in the range of 20% to 95% (i. E. Have boiling points below the residual cut point) Can be used.

Main goal:

The present invention relates to all hydrocracking furnaces, namely:

• Maxi-naphtha hydrocracking with a residual point of generally 150 ° C to 190 ° C, preferably 160 ° C to 190 ° C, usually 170 ° C to 180 ° C,

• maxi-kerosene hydrocracking with a residual point of generally 240 ° C to 290 ° C, usually 260 ° C to 280 ° C,

• It may also be used in a maxi-gas oil hydrocracking furnace with a residual point of generally 340 ° C to 385 ° C, usually 360 ° C to 380 ° C.

Embodiments:

Hydrocracking / hydrogen conversion processes using catalysts according to the present invention include conversion and pressure ranges from mild hydrocracking to high pressure hydrocracking.

The term " mild hydrocracking "generally refers to hydrocracking which results in less than 40% moderate conversion and operates at low pressure, typically 2 MPa to 9 MPa. The hydrocracking catalyst may be used alone, in single or more fixed bed catalyst beds, in one or more reactors, with a "once-through" hydrocracking layout, optionally with or without liquid recycle May be used in connection with a hydrogen purification catalyst located upstream of the hydrocracking catalyst.

Hydrocracking may be operated at high pressure (at least 10 MPa).

In a first variant, the hydrocracking may be operated according to a hydrocracking layout known as a "two-step" layout with intermediate separation between the two reaction zones; At a given stage, the hydrocracking catalyst may be used in one or both reactors, either with or without a hydrogen purification catalyst located upstream of the hydrocracking catalyst.

In a second variant, what is known as "perfusion-type" hydrocracking may be practiced. This variant generally includes intense hydrogen purification initially intended to effect hydrogenated denitrification and hydrodesulfurization of intense feed prior to delivery to the appropriate hydrocracking catalyst, especially when it comprises zeolite. This intense hydrogen purification of the feed causes only a limited conversion of this feed to the harder fraction. Therefore, still insufficient conversion must be supplemented in the more active hydrocracking catalyst.

The hydrocracking section may comprise one or more layers of the same or different catalysts. Alumina or silica-alumina or basic zeolite supplemented with at least one hydrogenation metal of the group VIII, optionally with at least one metal of the group VIB, preferably a basic amorphous solid, for example, when the preferred products are intermediate distillates Is used. The basic zeolite is comprised of silica, alumina and one or more exchangeable cations such as sodium, magnesium, calcium or rare earths.

When gasoline is the main desired product, the catalyst generally consists of a small amount of metal of group VIII, and more preferably crystalline zeolite with a metal of the group VIB precipitated.

The zeolites which may be used are natural or synthetic and may be selected, for example, from X, Y or L zeolites, spore-sites, mordenites, erionites or chabazites.

Hydrocracking may also be carried out in conjunction with a hydrogen purification catalyst located in the fixed bed or boiling layer reactor upstream of the hydrocracking catalyst, optionally in one or more boiling bed reactors, irrespective of the liquid recycle of the unconverted fraction have. The boiling layer is operated with the withdrawal of the consumed catalyst and the daily addition of fresh catalyst to keep the catalyst activity stable.

Liquid / gas separation (4):

The separator 4 separates the liquid and gas present in the effluent from the hydrocracking unit. Any type of separator capable of effecting this separation may be used, for example a flash drum, a stripper, or even a simple distillation column.

Discrimination (12):

The fractionation section generally consists of a plurality of plates and / or one or more columns comprising an inner packing, which may preferably be operated in a countercurrent mode. These columns are usually stripped steam and contain reboilers to facilitate vaporization. It is possible to separate hydrogen sulfide (H ₂ S) and hydrogen sulfide (H ₂ S) from the effluent as well as hydrocarbon oils having boiling points in gasoline, kerosene and gas oil ranges, together with heavy fractions recovered from the bottom of the column, Can be used to separate light components (methane, ethane, propane, butane, etc.).

Examples:

Example 1:

This embodiment is based on the configuration of Fig. Two samples from operating industrial units based on the configuration of FIG. 1 were analyzed. The characteristics are listed in Table 1 below.

It should be noted that, due to the configuration, the streams 15a, 16, 18, 23 have exactly the same characteristics.

The discrimination of stream 11 in column 12 was computer simulated using PRO / II version 8.3.3 software, available from SimSci. The physical and analytical properties of the generated streams were simulated and compared with the physical and analytical properties of the actual samples.

The operating conditions for the columns used in the simulations are listed in Table 2 below.

1: specific gravity SG = ρ _sample at 20 ° C / ρ _H20 at 4 ° C, where ρ is density expressed in g / cm 3

Beginning with the characteristics of the stream 11 entering the fractional column (see Table 1), the PRO / II simulation was able to set the characteristics of the stream 15 from the fractional column; In particular, the HPNA distribution could be modeled.

Based on these results, the inventive arrangements were simulated. The results are set forth below for the arrangement according to the invention.

Example 2: Construction of Figure 2 (according to the invention)

Table 3 below provides the characteristics of streams 11, 18 and 24 in the configuration of FIG. 2 obtained from PRO / II simulation. The operating conditions used in the simulations are listed in Table 4.

1: specific gravity SG = ρ _sample at 20 ° C / ρ _H20 at 4 ° C, where ρ is density expressed in g / cm 3

Compared to the configuration of FIG. 1, the configuration of FIG. 2 can be used to maximize the amount of HPNA (5435 ppm by weight compared to 902 ppm by weight in the configuration of FIG. 1) in the unconverted fraction purged through line 24 have. At the same time, the amount of HPNA was minimized in the stream returned to the reaction section via line 18 (613 ppm by weight compared to 902 ppm by weight in the configuration of Figure 1), which reduced the amount of HPNA by 32.0%.

In addition, the ratio of the refractory and toxic heavy HPNA (naphtho [8,2,1 abc] coronene + ovalene) compared to the total amount of HPNA in the stream returned to the reaction section is shown in Figure 36.3 (26.3%) than the configuration of Fig. 2 (Fig. 2). This not only has less total HPNA in the stream returning to the reaction section via line 18, but also the ratio of refractory and toxic heavy HPNA (naphtho [8,2,1 abc] coronene + ovalene) Indicating that it is lower.

In addition, this configuration can minimize the amount of gas oil sent to the reaction section via line 18 because the amount of gas oil returned to the reaction section is only 6.1 wt.% Compared to 10.9 wt.% In the configuration of FIG. %.

Claims (13)

A process for hydrocracking an oil feed comprising at least 10% by volume of compounds boiling above 340 < 0 > C,
The hydrocracking step comprises the hydrocracking step followed by the separation of the gas from the selectively hydrocracked effluent after the hydrocracking step and the subsequent fractionation of the effluent from which at least one distillate and reside has been separated Wherein a portion of the residual oil is recycled to the hydrocracking step and the fractionating step comprises distillation in a column with plates, wherein in the column:
The at least partially vaporized effluent is fed to the column through a feed plate,
The distillate is withdrawn from the level of the drawing plate,
The residual oil is discharged at the discharge point,
And the stripping gas is injected at an injection point located below the feed plate,
In the above method
A portion of the stream present at the level of at least one plate located between the feed plate and the plate for withdrawing the heaviest distillate fraction is withdrawn from the column,
All or a portion, preferably all, of said withdrawn stream is stripped in an external stripping step by a stripping gas in the presence of a portion of the residual oil discharged from said column, a gas effluent and a liquid fraction are obtained,
And all or part, preferably all, of the separated gas effluent is recycled to the column,
And all or part, preferably all, of said liquid fraction is recycled to said hydrocracking step,
And wherein residual oil is purged in said stripping step. The method according to claim 1,
Wherein a portion of the stream located above the level of the plate located on the feed plate and proximate to the feed plate, preferably at a level of the plate closest to the feed plate, is withdrawn from the column. 3. The method according to claim 1 or 2,
Wherein the withdrawn stream has an HPNA concentration of less than 500 ppm by weight, preferably less than 350 ppm by weight. 4. The method according to any one of claims 1 to 3,
Wherein the withdrawn stream has a ratio of at least 70 wt% unconverted hydrocarbons, preferably at least 80 wt% unconverted hydrocarbons. 5. The method according to any one of claims 1 to 4,
Wherein all or a portion, preferably all, of the gas effluent is recycled to the column below the feed plate. 6. The method according to one of claims 1 to 5,
Wherein the gas effluent is recycled as stripping gas, preferably as the sole stripping gas, to the column. 7. The method according to any one of claims 1 to 6,
Wherein all or a portion, preferably all, of the liquid effluent separated in the stripping step is directly recycled to the hydrocracking step. 8. The method according to any one of claims 1 to 7,
Wherein the stripping gas, optionally injected into the fractionation step, into the external stripping step is steam at a pressure preferably in the range of 0.2 to 1.5 MPa. 9. The method according to any one of claims 1 to 8,
Wherein a portion of the residual oil discharged from the column is recycled to the hydrocracking step. As a facility,
- a hydrogenolysis section (2) having an inlet line (1) for the feed and an inlet line (8) for hydrogen,
Optionally followed by a zone (4) for separating the effluent to separate the gas fractions,
Followed by a fractionation section (12) comprising at least one distillation column with plates, said column comprising:
at least one line (11) for the introduction of at least partially vaporized hydrocracked effluent into at least one feed plate,
o at least one line (14) for withdrawing at least one distillate from the level of the withdrawal plate,
o at least one line (15a) for discharging residues,
And at least one line (19) for injecting stripping gas, the injection point being located below said feed plate,
The facility includes:
At least one line (20) for withdrawing a portion of the stream present at the level of the at least one plate located between the feed plate and the plate for withdrawing the heaviest distillate fraction,
A line (16) for introducing a portion of the residual oil discharged from the column, a line (26) for injecting the stripping gas, an outlet line for the gas effluent (22), and an outflow line (27) for the liquid fraction, the stripper (25) outside the column,
And a line (22) for recirculating all, or preferably all, of said gas effluent to said column,
A line 27 for recirculating all, or preferably all, of the liquid fraction to the hydrocracking step,
- a line (24) for purging a portion of said residue. 11. The method of claim 10,
Lines (22, 19) are merged and said gas effluent is said stripping gas. The method according to claim 10 or 11,
Wherein the drawing plate (20) is at a level of the plate closest to the feeding plate. 13. The method according to one of claims 10 to 12,
Further comprising at least one line (23, 18) for recycling a portion of the residual oil discharged from the column to the hydrocracking step.

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